More tests in the test matrix

[nstarman]

Thanks for the great package, I use it frequently.
It would be great if the test matrix came with uv's --resolution=lowest-direct for testing the minimum versions of all dependencies. Right now I believe only the most recent versions of dependencies are tested.

[henryiii]

I've mostly avoided adding uv-only features. First a section explaining how to set this up would need to be added, then it possibly could be added. It does take some care, though; for example I've been trying to work it out at scikit-build/scikit-build-core#679 for a while. Not sure if it's a great idea to auto-include for everyone, but it should at least be in the guide!